Hypoxia upregulates MAPK(p38)/MAPK(ERK) phosphorylation in vitro: neuroimmunological differential time-dependent...

In mammalian cells, responses to hypoxia at the molecular transduction level are hallmarks of adaptation and survival under oxygen deprivation conditions. In this study, the protein expression patterns of mitogen-activated protein kinases (MAPKs) are investigated under hypoxia in primary cortical neurons and in a model of organotypic hippocampal slices in neonatal Sprague-Dawley rats. Abrupt fluctuations in MAPK expression can occur during anoxia, hypoxia, and relative hyperoxic shifts (e.g., reoxygenation); therefore, phosphorylation and dephosphorylation states could be crucial factors in metabolic reorganization for withstanding anaerobiosis. Whole cellular protein extracts were analyzed for the phosphorylation of MAPKp(p38) and MAPK(ERK-1/2 (p44/p42)) at threonine and tyrosine residues (Thr(180)/Tyr(182)) at different time periods of hypoxic exposure relative to a fixed normoxia control. The phospho-MAPK(p38) (p-MAPK(p38)) to MAPK(p38) relative unit ratio revealed that MAPK(p38) expression increased in cortical neurons after 5 and 10 min, but decreased abruptly afterwards (20 - 120 min). The expression of phospho-MAPK(ERK-1) (p-MAPK(ERK-1/p44)), however, decreased whereas that of p-MAPK(ERK-2/p42) increased compared to normoxia. In rat hippocampal slices (RHS), the expression of p-MAPK(p38) was slightly but significantly higher in hypoxia, whereas the expression of p-MAPK(ERK-2/p42) increased and that of p-MAPK(ERK-1/p44) was intangible. This indicates that in cortical neurons hypoxia differentially upregulated the phosphorylation activation states of MAPK(p38) and MAPK(ERK-1/2 (p44/p42)), whereas in the RHS model MAPK(p38) and MAPK(ERK-2/p42), but not MAPK(ERK-1/p44), phosphorylation states were upregulated in response to hypoxia. The neuroimmunological molecular patterns of the differential MAPK phosphorylation in vitro and ex vivo in response to hypoxic shift indicated a significant role for these kinases in cellular adaptation to oxygen deprivation, and thereby may identify physiologic and neuroprotective responsive signaling cofactors and pathways in cortical and hippocampal neurons during hypoxia.